Historically, door frames and doors were made of wood. Wood has the advantages of being easily worked in the field using hand tools, can be stained or painted to match other wood trim or panelling in a room, and has good screw holding ability, permitting the secure mounting of hinges, strike plates, knobs and latches as well as other hardware, such as door closing devices.
One significant drawback of wood is its poor resistance to fire. With the increased emphasis on fire retarding properties of building materials, particularly commercial structures, as evidenced by modern building codes, wooden door frames are now utilized principally in residential construction.
In addition to its failure to meet fire test standards, there are other disadvantages of wood for use as a door framing material. The supply of clear wood stock is limited and costs have risen as a result. Techniques have been developed to fabricate longer wood members from a plurality of short pieces of clear wood stock but these techniques introduce additional steps and equipment and hence higher costs.
Other disadvantages of wood include its tendency to deform and even rot under moist circumstances, and it is subject to scarring from even minor impacts. Refinishing can also be troublesome, since scraping or sanding can, if not carefully controlled, deform the planar surfaces.
In view of the above, and particularly due to building codes requiring fire retardant doors and door frames, steel has become the material of choice for door frames where fire retardant properties are required. Although steel door frames do readily pass the required fire and hose stream tests, they suffer from other shortcomings. Steel cannot be readily worked at the building site and hence even minor adjustments such as to a door frame height, for example, cannot be readily accomplished in the field.
Furthermore, steel frames are typically prefabricated by welding, making handling difficult and taking up more shipping space than would be required if the frame members could be shipped in a knocked down condition. In addition, steel frames cannot be stained to match the remaining woodwork in a room and accordingly must either be painted or treated with applications which simulate a wood finish.
Because of its typical thin sections, steel presents complications in attaching hardware, and recesses for hinges and strike plates must be prefabricated, limiting the options at the work site. Finally, although steel door frames are highly resistant to denting, finishes are apt to chip upon impact due to the non-resilient nature of the steel.
There is accordingly a need for a door frame which provides adequate fire resistance at a relatively low cost, which can be easily modified at the construction site and which has good screw holding properties as well as an attractive finished appearance.